Image 1: A welcoming sign at the Kilimanjaro Christian School of Optometry
Today we met at the Kilimanjaro Christian Medical Center (KCMC) School of Optometry and discussed the challenges facing optometry programs in Eastern Africa. Once again I mentioned the issue of spectacle fabrication, one challenge we have been facing at the Masinde Muliro University of Science and Technology. One of the faculty members said, “It’s easy. Let me show you how to do it. We use simple and inexpensive technology available all around the world.” We went next door to the optical shop.
Image 2: Laying out the spectacle lenses. Here one lens, in the optometrists hands, has already been roughly completed, while the other lens on the cloth is awaiting preparation.
The first step is to find and mark the optical center of the of the lens using a lensometer. Lensometers are not too expensive and are usually readily available. The lens blanks are usually 60 to 70 millimeters (mm) in diameter, and can be made of plastic (CR-39) or glass. It is important to know the interpupillary distance (IPD) of the patient which is the distance between the centers of the pupils. This distance is easily measured using a ruler with the patient present and is usually between 50 and 70 mm, depending mostly on the width of the nose and age of the patient. The optometrist then measures the frame to be used, taking note of the bridge width (B). Using the formula of (IPD – B)/2, and an outline of the shape of the frame, the optometrist can calculate the distance from the inner nasal edge of the spectacle aperture to the optical center of the lens. The optometrist then uses a marking pen to outline size and shape of the frame aperture in relation to the optical center of the lens. It is important to place the optical center of the lens in front of the pupil center. The higher the prescription, the more crucial the optical center placement.
Image 3: The optometrist uses a glass cutter tool to etch the glass. The purpose is to remove the excess glass on the periphery of the lens.
Image 4: The optometrist uses pliers to grab the periphery of the lens and carefully remove the excess glass. He puts on safety glasses for this step to avoid eye injury.
Image 5: The optometrist uses a manual grinding wheel to remove the excess glass and smooth the periphery of the lens. He is careful to grind the lens to the correct shape, making a beveled smooth lens edge. This process is called lens edging.
Image 6: Once both lenses have been edged, the plastic frame is heated, and the lenses are carefully inserted into the frame, usually from the front. The whole process takes about a half hour. Metal frames require more precision because metal is less forgiving than plastic. Rimless frames using nylon line require a special indented lens edge that is more difficult to fabricate by hand. The optometrist proudly shows his handiwork. It is in this way that high quality spectacles can be created at very low cost. All that is needed is a bank of lens blanks of varying power, plastic frames of varying sizes and shapes, and the tools and instruments mentioned here. Of course, knowledge of the process and experience is very important. Novice lens edgers tend to break a lot of lenses.
When I was an optometry student from 1989 through 1992, we learned how to complete this process although we did not spend much time on it. Now the spectacle fabrication process is rarely completed by optometrists in the United States, and is usually done by opticians using automated equipment. The KCMC School of Optometry has the more advanced equipment normally used in the United States, but they wanted to show me how to get started fabricating spectacles when the more expensive equipment is not available. This process could be very helpful at the Masinde Muliro University of Science and Technology School of Optometry, given that we currently do not have a spectacle fabrication laboratory.
Image 7: After showing me how to fabricate spectacles using inexpensive and readily available materials, we sat down and spent two hours discussing slit lamp biomicroscopy techniques.
The exchange of ideas and information at the KCMC School of Optometry has been very stimulating and rewarding.